1. Field of the Invention
This invention relates to a system of a hydraulic actuator for operating a valve between open and closed positions and the control system used to regulate the operation of the actuator. This system is particularly suited for operation of ball valves used in the oil and gas industry. These ball valves are typically used in gas pipelines to control the flow of gas through the pipeline. The actuator of the present invention uses gas pressure from the pipeline to power the actuator. In the event gas pressure from the pipeline is unavailable or inaccessible, a pair of manual hand pumps are incorporated to allow operation of the actuator and valve.
Prior actuators utilizing the gas pressure of the pipeline as a power source typically have a double acting piston upon which the gas acts to drive the actuator and hence the valve to be opened or closed. These actuators have vented the gas pressure from one side of the double acting piston as gas pressure is applied to the other side of the piston. This venting is necessary to ensure that equal pressure is not acting on both sides of the piston simultaneously. In this event, the force acting on both sides of the piston would balance and the actuator would fail to operate or be “pressure locked” as commonly referred to in the industry.
As a result of the need to vent each side of the actuator piston to ensure proper operation, the gas pressure is usually vented to atmosphere. This gas is not a pure gas but in fact has hydrocarbon liquids entrained in the gas, known as condensate in the industry. When this venting to atmosphere occurs, the hydrocarbon liquid condensate condenses and becomes a sticky, unsightly oily residue on the ground adjacent the valve and actuator. In recent years this venting to the atmosphere of the gas has raised environmental concerns due to possible contamination of the ground and groundwater by this oily residue.
Another concern with prior valve, actuator and control system assemblies has been the interface and operation of the manual hand pumps that are required to operate the actuator and valve when gas pressure from the pipeline is not available. This may occur during new installations when the pipeline has not been filled with gas yet and opening or closing of the valve is needed. Other times when maintenance is to be performed on the valve or actuator, the pipeline must be bled of gas pressure as a safety precaution. When it is desired to operate the valve prior to subsequent pressurization of the pipeline, the ability to operate the valve and actuator manually is required. Prior valve, actuator and control system assemblies have had problems in their design and operation that allowed possible scenarios in which pressurization of the pipeline and thus the actuator, could result in inadvertent operation of the actuator while manual operation of the actuator was occurring and possible injury to an operator. It is therefore desirable to have a valve, actuator and control system assembly that allows minimizing the size of the actuator and operation of the control system in a manual mode that automatically prevents accidental operation by pipeline pressure. The valve, actuator and control system of the present invention offers such novel features.
2. Description of Related Art
U.S. Pat. No. 6,231,027 B1 to G. S. Baker et al. shows a valve actuator that utilizes a variable helix angle to generate greater operating torque near the end of its travel.
A subsea rotary adjusting device for valves is disclosed in PCT International Publication No. WO 02/37008 A1 to K. Biester et al. The device utilizes a helical slot in a sleeve to translate axial motion into rotary motion.
PCT International Publication No. WO 03/025428 A1 to K. Biester et al. shows a travel multiplying device utilizing three concentric pipes with spherical linking elements to magnify relative longitudinal motion between adjacent pipes.